PROJECT SUMMARY/ABSTRACT This project is a proof of principle of systems toxicology, a new approach to chemical safety evaluation that integrates molecular, cellular, and physiological data in the context of a genetically diverse animal model to develop testable hypotheses about the key molecular events leading to adverse outcomes following chemical exposure. The project aims to capitalize on the potential of two powerful population-based model organism resources, the Collaborative Cross (CC) and Diversity Outbred (DO) mice, to study the role of genetics in conferring susceptibility to chemical exposures. Through an integrated set of experiments using arsenic exposure in mice and cell lines, the molecular genetic basis of toxicological responses will be evaluated. This project will test the hypothesis that genetic analysis in the context of a quantitative environmental perturbation will reveal multiple, novel, and diverse biochemical networks that respond to chemical exposure. The proposed integrated set of experiments will enable the discovery and validation of adverse outcome pathways through three specific aims. Aim 1 will evaluate study designs for animal testing with genetically diverse DO mice including sample size requirements for toxicity evaluation. G x E genetic loci will be mapped and incorporated into predictive computational models, and testable hypotheses will be proposed for validation. Aim 2 will conduct a parallel, population-level arsenic exposure study of in vitro primary cell cultures to identify genetic factors underlying susceptibility and resistance using physiologically informative cellular phenotypes. The data generated in the in vitro arsenic exposure study will allow determination of the extent to which cytotoxicity, genotoxicity, and oxidative stress in cellular assays are physiologically informative for the discovery of molecular pathways that drive susceptibility and/or response in the whole organism. Aim 3 will identify key mechanisms in renal arsenic toxicity. This study will generate a model for the effect of arsenic exposure on the kidney to predict outcomes that are contingent on genetic background. Collectively, this new approach to toxicology using DO mice will address fundamental biological questions by combining chemical interventions with genetic variation. It will establish causal pathways across multiple levels of molecular and physiological outcomes to yield results with relevance to clinical translation.